1. Field of the Invention
This invention relates to test equipment for semiconductor devices and, more particularly, to a transmission-line pulser circuit for testing semiconductor devices.
2. Prior Art
A transmission line pulsing technique is used to generate short-duration, high current pulses to probe-test electrostatic discharge (ESD) performance of a semiconductor device. The transmission line pulsing technique charges the distributed capacitance of a transmission line and then discharges the line to produce a voltage pulse having a duration time equal to 2 l/c, where 1 is the length of the line and c is the propagation velocity of the transmission line.
In previous designs of transmission-line pulser test equipment for probe-testing of semiconductor devices, a so-called recharge transient problem has arisen. For the recharge transient problem, a charge-storing element, such as the capacitance of a transmission line, is switched between a high voltage source and a device under test (DUT). The transmission line, which provides the charge-storage capacitance, has one terminal connected to ground and its other terminal connected to the movable arm terminal of a double-pole, single-throw relay. One contact of the relay is connected to the high-voltage source through a high resistance and the other contact of the relay is connected to a probe connected to a device under test (DUT). A small shunt capacitance exists between the two relay contacts, so that, when the transmission line is connected to the high-voltage source to charge the charge-storage capacitance of the transmission line, the shunt capacitance across the relay contacts allows a displacement current to travel to the DUT. This displacement current is given by I.sub.x (t)=C.sub.x dr/dr, where C.sub.x is the small shunt capacitance across the two relay contacts. The effect of this is to put an uncontrolled amount of electrical stress on the DUT, which skews the effect of a subsequent test pulse.
Another problem associated with measurement of a DUT is the effect of leakage current caused by a voltage measurement probe used to measure voltage across the DUT. A constant voltage source forces a voltage on the DUT and the resultant leakage current through the DUT is then measured. The voltage probe measures the voltage applied by the constant voltage source across the DUT. If the resistance of the DUT is much greater than the resistance of the voltage probe, more current will flow through the lower resistance of the voltage probe than through the higher resistance of the DUT. As a result, the current flowing through the voltage probe will mask the leakage current through the DUT.
Consequently, the need has arisen for a technique for testing a semiconductor device which prevents relay recharge transients and which prevents voltage-probe leakage currents.